FIG. 1 illustrates transmission resources used for uplink transmission. Hereinafter, a basic structure of transmission resources used during uplink transmission will be described with reference to FIG. 1.
Uplink transmission is based on an orthogonal frequency division multiplexing access (OFDMA) structure, in which a frequency axis and a time axis are allocated in a certain unit. Referring to FIG. 1, twelve subcarriers are defined as a single resource block (RB), which is a basic allocation unit, on a frequency axis while six long blocks (LB) and two short blocks (SB) are defined as a single transmission time interval (TTI) on a time axis. The SB has a length which is half of that of the LB on the time axis. Also, the SB has the number of subcarriers on the frequency axis, which is half of the number of subcarriers of the LB, and has a subcarrier space which is twice of that of the LB. The SB is generally used for pilot signals (or reference signals).
There may be a case where communication is performed by directly inserting signals generated form sequences to a channel. For example, examples of the sequences include CAZAC (Constant Amplitude Zero AutoCorrelation) sequences, such as GCL (Generalized Chirp Sequence) CAZAC sequence and Zadoff-Chu CAZAC sequence, and gold code. The CAZAC sequences are mainly used in 3GPP, and the gold code is mainly used in WCDMA. Particularly, the CAZAC sequence, which has a certain size suitable for power boosting and has excellent correlation characteristics suitable for synchronization acquisition, will be described below.
Two types are mainly used as the CAZAC sequences, i.e., GCL CAZAC sequence and Zadoff-Chu CAZAC sequence as described above.
First of all, the Zadoff-Chu CAZAC sequence is given as follows.
                                          g            p                    ⁡                      (            n            )                          =                  {                                                                                                                                        ⅇ                                                                              -                            j                                                    ⁢                                                                                    2                              ⁢                              π                                                        M                                                    ⁢                                                      1                            2                                                    ⁢                                                      pn                            2                                                                                                                                                              when                        ⁢                                                                                                  ⁢                        N                        ⁢                                                                                                  ⁢                        is                        ⁢                                                                                                  ⁢                        even                                                                                                                                                ⅇ                                                                              -                            j                                                    ⁢                                                                                    2                              ⁢                              π                                                        M                                                    ⁢                                                      1                            2                                                    ⁢                                                      pn                            ⁡                                                          (                                                              n                                +                                1                                                            )                                                                                                                                                                                                                    when                          ⁢                                                                                                          ⁢                          N                          ⁢                                                                                                          ⁢                          is                          ⁢                                                                                                          ⁢                          odd                                                ,                                                                                            ⁢                                                                  ⁢                n                            =              0                        ,            1            ,            …            ⁢                                                  ,                          N              -              1                                                          [                  Equation          ⁢                                          ⁢          1                ]            
In the above Equation, N is a length of a sequence, and p is a sequence index and has a value of 1 as a common factor with N. This Zadoff-Chu CAZAC sequence satisfies periodic auto-correlation characteristic for a fixed value p. In other words, except that the Zadoff-Chu CAZAC sequence performs correlation for its sequence as it is, the Zadoff-Chu CAZAC sequence always has a correlation value of ‘0’ with a sequence which has undergone cyclic shift. The Zadoff-Chu CAZAC sequence is not orthogonal with a sequence having another p value but has a low cross-correlation value. If N is a prime number, N−1 sequences can be generated, and a cross-correlation value between the generated sequences is 1/√{square root over (M)}.
The GCL CAZAC sequence is given by the Equation 2 as follows.c(n)=gp(n)b(n mod m), n=0, 1, . . . , N−1  [Equation 2]
gp(n) is ZC sequence having a length of N, and b(n mod m) is an orthogonal modulation sequence such as Hadamard or DFT. The GCL CAZAC sequence has a length which should satisfy N=sm2.
In addition to the above CAZAC sequences, various CAZAC sequences exist.
Generally, although a user uses the entire of one resource block, since the amount of a control signal such as CQI (channel quality information) is not sufficient, the control signal can be allocated for several users within one resource block. Accordingly, a multiplexing method for transmission of a control signal between users is required.